Hafnium Silicide Target for Forming Gate Oxide Film, and Method for Preparation Thereof

ABSTRACT

A hafnium silicide target is provided. The target is used for forming a gate oxide film composed of HfSi 1.02-2.00 . The target material is superior in workability and embrittlement resistance and is suitable for forming a HfSiO film and HfSiON film that may be used as a high dielectric gate insulation film in substitute for a SiO 2  film. A method of manufacturing the above referenced hafnium silicide target is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. application Ser. No.10/480,319, which is the National Stage of International Application No.PCT/JP02/05547, filed Jun. 5, 2002, which claims the benefit under 35USC §119 of Japanese Application No. 2001-217586, filed Jul. 18, 2001and Japanese Application No. 2002-105905, filed Apr. 9, 2002.

BACKGROUND OF THE INVENTION

The present invention relates to a hafnium silicide target superior inworkability and embrittlement resistance, and suitable for forming aHfSiO film and HfSiON film that may be used as a high dielectric gateinsulation film, and to the manufacturing method thereof. Moreover, theunit of “ppm” as used in this description shall mean wtppm in all cases.

The film thickness of a dielectric gate insulation film largelyinfluences the performance of a MOS transistor, and it is essential thatthe interface with the silicon substrate is electrically smooth and thatthe mobility of the carrier does not deteriorate.

Conventionally, a SiO₂ film has been used as this gate insulation film,and was the most superior in terms of interfacial quality. In addition,there is a characteristic in that the thinner the SiO₂ film used as thisgate insulation film, the number of carriers (that is, electrons orelectron holes) increases, and the drain current also increases thereby.

From the foregoing circumstances, each time the power supply voltagewould decrease as a result of miniaturizing the wiring, the gate SiO₂film has been consistently formed as thin as possible within a rangethat would not deteriorate the reliability of dielectric breakdown.Nevertheless, a tunnel leakage current flows directly when the gate SiO₂film is formed of a thickness of 3 nm or less, and a problem arises inthat this film would not function as an insulation film.

Meanwhile, although attempts are being made to miniaturize thetransistor, so as long as there are limitations in the film thickness ofthe SiO₂ film, which is the gate insulation film as described above,miniaturization of the transistor loses its significance, and a problemarises in that the performance is not improved.

Moreover, in order to lower the power supply voltage of the LSI as wellas lower the power consumption, it is necessary to make the gateinsulation film even thinner. Nevertheless, since there is a problemregarding the gate dielectric breakdown when the film thickness of theSiO₂ film is made 3 nm or less as described above, thinning of the filmhad a limitation in itself.

In light of the foregoing circumstances, a high dielectric gateinsulation film is being considered lately as a substitute for the SiO₂film. And, the HfSiO film and HfSiON film are attracting attention asthis type of high dielectric gate insulation film.

This high dielectric gate insulation film is a comparatively thick film,and is capable of acquiring a capacity equivalent to the SiO₂ film, andis characterized in that it is able to suppress the tunnel leakagecurrent. Further, since this can be deemed as a film in which SiO₂ isadded to Hf, interfacial quality similar to that of SiO₂ can beexpected.

Thus, sought is a sputtering target capable of easily and stably forminga high-grade HfSiO and HfSiON high dielectric gate insulation film.

SUMMARY OF THE INVENTION

In order to overcome the foregoing problems, the present invention aimsto provide a hafnium silicide target superior in workability andembrittlement resistance, and suitable for forming a HfSiO film andHfSiON film that may be used as a high dielectric gate insulation filmin substitute for a SiO₂ film, and the manufacturing method thereof.

The present invention provides a hafnium silicide target for forming agate oxide film composed of HfSi_(1.02-2.00) In this composition ratio,however, Si:1.02 is not included. In other words, this implies that onlythe lower limit value of Si is 1.02 or more. This applies throughoutthis description.

Preferably, the above referenced hafnium silicide target contains amixed phase principally including a HfSi phase and a HfSi₂ phase and/orhas a relative density of 95% or more, an oxygen content of 500 to 10000ppm, and/or a zirconium content of 2.5 wt % or less. Preferably, theimpurities of the above referenced hafnium silicide target include C:300 ppm or less, Ti: 100 ppm or less, Mo: 100 ppm or less, W: 10 ppm orless, Nb: 10 ppm or less, Fe: 10 ppm or less, Ni: 10 ppm or less, Cr: 10ppm or less, Na: 0.1 ppm or less, K: 0.1 ppm or less, U: 0.01 ppm orless, and Th: 0.01 ppm or less. Further, the average grain size of theabove referenced target is preferably 5 to 200 μm.

The present invention is also directed to a method of manufacturing ahafnium silicide target for forming a gate oxide film, characterized inthat the powder of the composition composed of HfSi_(1.02-2.00) issynthesized, pulverized to be 100 mesh or less, and thereafter hotpressed at 1400° C. to 1535° C. Preferably, hot pressing is performed at150 to 2000 kgf/cm².

DETAILED DESCRIPTION OF THE INVENTION

A high dielectric gate insulation film comprising the quality as asubstitute for the SiO₂ film is formed by performing oxygen reactivesputtering to a HfSi target. This oxide film is considered to be ahybridization of an oxide film as represented with HfO₂.SiO₂ or a filmin which a part of the oxygen is replaced with nitrogen, and a targetwas usually demanded of a composition of Si/Hf=1.0. Generally, althoughthe composition ratio of Hf and Si is demanded to be a composition ratioclose to the target film, a Hf-rich oxide film tends to have a highrelative dielectric constant, a Si-rich oxide film has favorablecompatibility with a Si substrate and can easily become an amorphousstructure, and therefore possesses a characteristic of having a low leakcurrent.

In light of the above, it is necessary to consider and determine thebalance of the dielectric constant and leak current in accordance withthe purpose of use. Moreover, each manufacturing process of a device isdemanded of unique compatibility, and a material capable of arbitrarilychanging the composition ratio of Hf and Si as necessary is in demand.

When sintering the mixed powder of hafnium and silicon, in accordancewith the composition ratio, silicide phases such as a HfSi phase andHfSi₂ phase, and mixed crystals such as a Hf phase and Si phase areformed, but generally speaking, there is a problem in that these hafniumsilicide inter compounds are not able to obtain sufficient densityincrease during the sintering since they have a high melting point,become a sintered body of a porous texture, and thereafter become atarget with numerous generation of particles.

And, unless adjusting the hot pressing conditions, that is, the heatingtemperature and pressure in accordance with the composition ratio, atarget of an optimum density cannot be obtained.

Upon persevering to improve the increase in density, the presentinvention succeeded in obtaining a target suitable as a hafnium silicidetarget for forming a gate oxide film.

The present invention provides a hafnium silicide target for forming agate oxide film composed of HfSi_(1.02-2.00) in consideration of thebalance between the dielectric constant and leak current. This hafniumsilicide target comprises a mixed phase having a HfSi phase and a HfSi₂phase as principal phases, which eliminates the porous structure, andwhich has a relative density of 95% or more.

When the relative density becomes less than 95%, the brittlenessdeteriorates due to the lack of density, and the workability alsodeteriorates thereby. This also generates the increase of particlescaused by the fracture and scattering of fragile crystals. It istherefore preferable that the relative density be within the foregoingrange.

It is desirable that the oxygen content within the hafnium silicidetarget for forming the gate oxide film be 500 to 10,000 ppm. When oxygenis less than 50 ppm, there is a possibility that the target will igniteduring the manufacture thereof, and, contrarily, when oxygen exceeds10,000 ppm, oxygen within the target will deposit as an oxide and causeabnormal discharge during the sputtering, particles will increasethereby, and the product yield rate will decrease as a result thereof.

Further, it is preferable that the zirconium content within the targetbe controlled to 2.5 wt % or less. When the amount of zirconium exceeds2.5 wt %, process conditions such as voltage, current and substratetemperature during the reactive sputtering for forming the oxide filmwill vary greatly, and this is not preferable.

Moreover, it is preferable that impurities within the hafnium silicidetarget for forming the gate oxide film are C: 300 ppm or less, Ti: 100ppm or less, Mo: 100 ppm or less, W: 10 ppm or less, Nb: 10 ppm or less,Fe: 10 ppm or less, Ni: 10 ppm or less, Cr: 10 ppm or less, Na: 0.1 ppmor less, K: 0.1 ppm or less, U: 0.01 ppm or less, and Th: 0.01 ppm orless. This is because these impurities will become the contaminationsource to the gate electrode and lower Si substrate. In order tomanufacture a hafnium silicide target for forming a gate oxide filmsuperior in embrittlement resistance composed of HfSi_(1.02-2.00),powder of the composition composed of HfSi_(1.02-2.00) is combined andthereafter hot pressed at 1400° C. to 1535° C. If the temperature isless than 1400° C., the density will be insufficient, and if thetemperature exceeds 1535° C., this is not preferable since partialdissolution will begin to occur.

Upon combining the powder of the composition composed ofHfSi_(1.02-2.00), hafnium hydride powder and Si powder are prepared andmixed at a molar ratio of 1:1.02 to 1:2.00, and thereafter sintered at600° C.-800° C.

Although the use of Hf powder may also be considered, Hf powder is notpreferable since it has strong oxidizability, and, when pulverized,there is a problem in that it may ignite.

Therefore, hafnium hydride is used for preventing this kind of ignition.It is desirable that hafnium hydride powder and silicon powder are usedupon being pulverized under 100 mesh. The use of this fine powderenables the realization of high density at the time of sintering.

Dehydrogenation and silicide formation are conducted with the heatingprocess during the sintering described above. Dehydrogenation begins tooccur from around 600° C. Although sintering is conducted in a vacuum(1×10⁻⁴ to 1×10⁻² Torr), it becomes a slight hydrogen atmosphere fordehydrogenation.

Moreover, dehydrogenation is completed upon heating to a temperature of800° C., and, the portion that may ignite with the Hf metal is formedinto a silicide, or sintered to a degree without any fear of ignition(approximately 3 μm or larger).

As described above, by conducting dehydrogenation and forming a silicideat a low temperature during the thermal synthesis, grain growth can besuppressed, primary grain of the sintered powder remains fine, and maybe made into a high density during molding. If the sintered powderbecomes coarse, pulverization before sintering becomes difficult, andresults in residual coarse particles and deterioration in density.

Accordingly, a significant characteristic is yielded in that the crystalgrain growth can be suppressed since sintering is conducted at a lowtemperature, and the average crystal grain size of the hafnium silicidetarget for forming a gate oxide film can be made to be 5 to 200 μm. And,high densification can be achieved upon sintering.

With a target having an average crystal grain size of less than 5 μm, itis difficult to make the amount of oxygen 10,000 ppm or less, and thereis fear of ignition during the manufacturing process. Moreover, when theaverage crystal grain size exceeds 200 μm, since particles will increaseand the production yield rate will deteriorate, it is desirable that theaverage crystal grain size be set between 5 and 200 μm as describedabove.

High densification during sintering is enabled through the synthesis ofthe powder composed from the foregoing HfSi_(1.02-2.00) and hot pressingthis at 1400° C. to 1535° C.

The foregoing hot pressing temperature is a temperature immediatelyunder the liquid phase generation of the synthesized powder, and thistemperature range is important for the sintering. This enables therealization of a high density hafnium silicide target having a relativedensity of 95% or more.

The high density hafnium silicide target of the present invention yieldsan effect in preventing the generation of particles caused by the poresduring sputtering.

EXAMPLES

Next, the Examples are explained. Further, these Examples are merelyillustrative, and the present invention shall in no way be limitedthereby. In other words, the present invention shall include all othermodes or modifications other than these Examples within the scope of thetechnical spirit of this invention.

Example 1

A synthesized powder of HfSi_(1.1) was obtained by mixing HfH₂ powderunder 100 mesh and Si powder under 100 mesh and heating this at 800° C.in a vacuum, whereby dehydrogenation reaction and silicide syntheticreaction were conducted at once.

This hafnium silicide powder was pulverized to obtain hafnium silicidepowder under 100 mesh. Here, it is also possible to add pre-synthesizedhafnium silicide powder. It has been confirmed with XRD that thishafnium silicide powder is composed of a mixed phase including a HfSiphase and HfSi₂ phase.

A sintered body having a density of 99.3% was obtained by hot pressingthis silicide powder under the condition of 300 kg/cm²×2 hours at 1500°C. This was further machine processed to prepare a target of φ 300mm×6.35 mmt. Texture with hardly any pores was obtained thereby.

Sputtering was performed with the target prepared as described above,and, upon measuring the particles on a 6 inch wafer, only a total of 12particles having a measurement of 0.2 μm or larger were found, and thegeneration of particles decreased considerably.

A hafnium suicide target superior in workability and embrittlementresistance was obtained as a result of the above. Further, since thistarget may be employed in wet processing, there is no longer any fear ofignition during the processing.

Example 2

A synthesized powder of HfSi_(1.5) was obtained by mixing HfH₂ powderunder 100 mesh and Si powder under 100 mesh and heating this at 800° C.in a vacuum, whereby dehydrogenation reaction and silicide syntheticreaction were conducted at once.

This silicide powder was pulverized to obtain hafnium silicide powderunder 100 mesh. Here, it is also possible to add pre-synthesized hafniumsilicide powder. It has been confirmed with XRD that this hafniumsilicide powder is composed of a mixed phase including a HfSi phase andHfSi₂ phase.

A sintered body having a density of 99.8% was obtained by hot pressingthis hafnium silicide powder under the condition of 300 kg/cm²×2 hoursat 1420° C. This was further machine processed to prepare a target of φ300 mm×6.35 mmt.

Sputtering was performed with the hafnium silicide target prepared asdescribed above, and, upon measuring the particles on a 6 inch wafer,only a total of 18 particles having a measurement of 0.2 μm or largerwere found, and the generation of particles decreased considerably.

A hafnium silicide target superior in workability and embrittlementresistance was obtained as a result of the above. Further, there is nofear of ignition during the processing.

Example 3

A synthesized powder of HfSi_(1.9) was obtained by mixing HfH₂ powderunder 100 mesh and Si powder under 100 mesh and heating this at 800° C.in a vacuum, whereby dehydrogenation reaction and silicide syntheticreaction were conducted at once.

This silicide powder was pulverized to obtain hafnium silicide powderunder 100 mesh. Here, it is also possible to add pre-synthesized hafniumsilicide powder. It has been confirmed with XRD that this hafniumsilicide powder is composed of a mixed phase including a HfSi phase andHfSi₂ phase.

A sintered body having a density of 98.4% was obtained by hot pressingthis hafnium silicide powder under the condition of 300 kg/cm²×2 hoursat 1520° C. This was further machine processed to prepare a target of φ300 mm×6.35 mmt.

Sputtering was performed with the hafnium silicide target prepared asdescribed above, and, upon measuring the particles on a 6 inch wafer,only a total of 20 particles having a measurement of 0.2 μm or largerwere found, and the generation of particles decreased considerably.

A hafnium silicide target superior in workability and embrittlementresistance was obtained as a result of the above. Further, there is nofear of ignition during the processing.

Comparative Example 1

A synthesized powder of HfSi_(1.3) was obtained by mixing HfH₂ powderunder 100 mesh and Si powder under 100 mesh and heating this at 800° C.in a vacuum, whereby dehydrogenation reaction and silicide syntheticreaction were conducted at once. This silicide powder was pulverized toobtain hafnium silicide powder under 100 mesh. It has been confirmedwith XRD that this hafnium silicide powder is composed of a mixed phaseincluding a HfSi phase and HfSi₂ phase.

A sintered body was obtained by hot pressing this silicide powder underthe condition of 120 kg/cm²×2 hours at 1500° C. The obtained sinteredbody had a low density of 92.7%. This was further machine processed toprepare a target of φ 300 mm×6.35 mmt.

Since the density of this target is low, through-pores existed.Therefore, since it is extremely difficult to eliminate contamination ofthe working fluid during the processing upon manufacturing the targetemployed in manufacturing the actual device, it is not possible toperform wet processing. Therefore, in order to prevent ignition of theprocessing powder, special measures must be taken such as performing dryprocessing under an inert gas atmosphere.

Sputtering was performed with the target prepared as described above,and, upon measuring the particles on a 6 inch wafer, a total of 270particles having a measurement of 0.2 μm or larger were found. Inaddition, a plurality of protrusions referred to as nodules hadgenerated on the outer peripheral face of the target.

As described above, density cannot be improved when sintering at hightemperatures outside the scope of the present invention, and this alsoresulted in the generation of numerous particles.

Comparative Example 2

A synthesized powder of HfSi_(1.3) was obtained by mixing HfH₂ powderunder 100 mesh and Si powder under 100 mesh and heating this at 800° C.in a vacuum, whereby dehydrogenation reaction and silicide syntheticreaction were conducted at once.

This silicide powder was pulverized to obtain hafnium silicide powderunder 100 mesh. It has been confirmed with XRD that this hafniumsilicide powder is composed of a mixed phase including a HfSi phase andHfSi₂ phase.

A sintered body was obtained by hot pressing this hafnium silicidepowder under the condition of 300 kg/cm²×2 hours at 1380° C. Theobtained sintered body had a low density of 90.6%. This was furthermachine processed to prepare a target of φ 300 mm×6.35 mmt.

Since the density of this target is low, through-pores existed.Therefore, since it is extremely difficult to eliminate contamination ofthe working fluid during the processing upon manufacturing the targetemployed in manufacturing the actual device, it is not possible toperform wet processing. Therefore, in order to prevent ignition of theprocessing powder, special measures must be taken such as performing dryprocessing under an inert gas atmosphere.

Sputtering was performed with the target prepared as described above,and, upon measuring the particles on a 6 inch wafer, a total of 490particles having a measurement of 0.2 μm or larger were found. Inaddition, a plurality of nodules had generated.

As described above, density cannot be improved when sintering at lowtemperatures outside the scope of the present invention, and this alsoresulted in the generation of numerous particles.

The relative density of the respective targets in Examples 1 to 3 was95% or more. Further, the number of particles was 20 or less.Improvement in the relative density was achieved similarly under the hotpressing conditions of 1400° C. to 1535° C.

As described above, it has been confirmed that a hafnium silicide targetin which the Hf: Si ratio is 1:1.02 to 2.00 can be stably manufacturedunder the foregoing conditions while improving the density of thesintered body.

Contrarily, the relative density in Comparative Example 1 was low at92.7%. The result was inferior where the number of particles was 270 andnodules arose as a result thereof.

Moreover, the relative density in Comparative Example 2 was low at90.6%. The result was inferior where the number of particles was 490 andnodules similarly arose as a result thereof.

Accordingly, superiority of the Examples according to the presentinvention is evident, and it is further clear that the present inventionpossesses superior characteristics.

The present invention is characterized in that it is able to obtain ahafnium silicide target superior in workability and embrittlementresistance, and suitable for forming a HfSiO film and HfSiON film thatmay be used as a high dielectric gate insulation film in substitute fora SiO₂ film.

The present hafnium silicide target has a relative density of 95% ormore and is of high density, and possesses superior strength.

Moreover, the highly densified silicide target of the present inventionis capable of preventing the generation of particles arising from poresduring the sputtering and the generation of particles resulting from thefracture and scattering of brittle textures, and yields a significantadvantage in that it does not ignite during the processing ormanufacturing process of the target.

1. A method of manufacturing a hafnium silicide sputtering target foruse in forming a gate oxide film, comprising the steps of: synthesizinga powder of a composition made of HfSi_(1.02-2.00); pulverizing thepowder to be 100 mesh or less; and after said synthesizing andpulverizing steps, hot pressing the powder at 1400° C. to 1535° C. toform a sintered hafnium sputtering target that is made ofHfSi_(1.02-2.00), that contains a mixed phase principally including aHfSi phase and a HfSi₂ phase, and that has a relative density of 95% ormore.
 2. A method according to claim 1, wherein said hot pressing stepis performed at 150 to 2,000 kgf/cm².
 3. A method according to claim 2,wherein said hot pressing step is hot isostatic pressing (HIP).
 4. Amethod according to claim 1, wherein the sintered hafnium sputteringtarget formed consists of HfSi_(1.02-2.00).
 5. A method according toclaim 4, wherein the HfSi_(1.02-2.00) consists of a mixed phase of aHfSi phase and a HfSi₂ phase.
 6. A method according to claim 1, whereinthe sintered hafnium sputtering target formed has an oxygen content of500 to 10,000 ppm.
 7. A method according to claim 1, wherein thesintered hafnium sputtering target formed has a zirconium content of 2.5wt % or less.
 8. A method according to claim 1, wherein the sinteredhafnium sputtering target formed contains impurities including 300 ppmor less of C, 100 ppm or less of Ti, 100 ppm or less of Mo, 10 ppm orless of W, 10 ppm or less of Nb, 10 ppm or less of Fe, 10 ppm or less ofNi, 10 ppm or less of Cr, 0.1 ppm or less of Na, 0.1 ppm or less of K,0.01 ppm or less of U, and 0.01 ppm or less of Th.
 9. method accordingto claim 1, wherein the sintered hafnium sputtering target formed has anaverage grain size of 5 to 200 μm.
 10. A method of manufacturing ahafnium silicide sputtering target for use in forming a HfSiO or HfSiONhigh dielectric gate insulation film, comprising the steps of:synthesizing a powder of a composition consisting of HfSi_(1.02-2.00);pulverizing the powder to be 100 mesh or less; and after saidsynthesizing and pulverizing steps, hot pressing the powder at 1400° C.to 1535° C. to form a sintered hafnium sputtering target that consistsof HfSi_(1.02-2.00), that is a mixed phase consisting of a HfSi phaseand a HfSi₂ phase, and that has a relative density of 95% or more.
 11. Amethod according to claim 10, wherein said hot pressing step isperformed at 150 to 2,000 kgf/cm².
 12. A method according to claim 11,wherein said hot pressing step is hot isostatic pressing (HIP).
 13. Amethod according to claim 12, wherein the sintered hafnium sputteringtarget formed has an oxygen content of 500 to 10,000 ppm.
 14. A methodaccording to claim 13, wherein the sintered hafnium sputtering targetformed has a zirconium content of 2.5 wt % or less.
 15. A methodaccording to claim 14, wherein the sintered hafnium sputtering targetformed contains impurities including 300 ppm or less of C, 100 ppm orless of Ti, 100 ppm or less of Mo, 10 ppm or less of W, 10 ppm or lessof Nb, 10 ppm or less of Fe, 10 ppm or less of Ni, 10 ppm or less of Cr,0.1 ppm or less of Na, 0.1 ppm or less of K, 0.01 ppm or less of U, and0.01 ppm or less of Th.
 16. A method according to claim 15, wherein thesintered hafnium sputtering target formed has an average grain size of 5to 200 μm.